A monitoring device of the type named above is described in DE 101 00 522 A. The implement is equipped with several sensors for detecting vibrations generated by its components during operation. Furthermore, rotational speeds of individual components can be detected. The amplitudes and frequencies of the detected vibrations are allocated by a calculating device on the basis of the measured rotational speeds to individual components of the machine and compared with allocated comparison values. Alternatively, the vibrations are allocated to the components on the basis of their already known rotational speeds. The monitoring device enables recognition of defective components on the basis of the vibration spectrum that changes due to the defect.
However, the components of agricultural implements, especially combines, cause vibrations, which depend not only on their rotational speed and their state, but also on whether or not it is in contact with crops or other material to be processed, for example, when soil tilling or when spreading or distributing fertilizer, seed, or chemicals. This condition is to be considered when evaluating the vibration spectra. In DE 101 00 522 A, it is proposed to analyze the noise spectrum only occasionally, for example, when turning at the end of a field. However, then information is provided only over relatively short time periods, which, due to the short measurement time and the resulting uncertainty of the values Fourier-transformed into the frequency domain, is not always adequate for sufficiently error-free identification of defective components.
In DE 39 07 419 A, a method for acoustic detection of damage to a machine is described, in which the sound waves are detected only for predetermined operating conditions, such as rotational speed, stress, and temperature, and compared with predetermined limits. Here, depending on the selection of the predetermined operating conditions, only minimal amounts of data are detected.